The invention relates generally to threaded fasteners, and more particularly to improved anti-cross threading fasteners.
Threaded fasteners of the type including a helically threaded shaft portion are known generally and used widely. These include various threaded shaft members about which a nut or other member having a complementary threaded bore is installable. The threaded shaft members are formed often as bolts with a tool engagable, or wrenching end, to which a torque is applied for installation, but more generally may include any threaded shank protruding from an article or machine.
It is also known that threaded fasteners have a tendency to cross-thread during assembly. Cross-threading occurs generally due to angular and axial misalignment between the threaded members during assembly, and is particularly troublesome for unskilled laborers and automated assembly operations, resulting in reduced productivity and damaged components, which are generally not reusable. The problems associated with crossthreading have been recognized by others, and efforts have been made to eliminate or at least reduce the occurrence thereof.
U.S. Pat. No. 3,828,604 issued Aug. 14, 1974, entitled "Method and Apparatus for Forming Tips of Screws", and assigned commonly herewith, for example, discloses a method for making threaded fasteners having a curved tip portion which facilitates assembly thereof in a complementarily threaded bore.
WIPO International Publication No. WO 97/04241 entitled "Anti-Cross Threading Fastener", published on Feb. 6, 1997 discloses a fastener with two or more relatively narrow diameter and curved transitional threads, which may reduce cross-threading when the angular and axial misalignments are not excessive. In Publication No. WO 97/04241, however, the threaded shaft portion proximate the tip end thereof limits the angular misalignment for which the curved threads compensate. In other embodiments disclosed in Publication No. WO 97/04241, a non-threaded fastener tip end, or dog point, portion having a reduced diameter similarly limits the angular misalignment for which the curved threads compensate.
The present invention is drawn toward advancements in the art of threaded fasteners generally, and more particularly to novel improvements in anti-cross threading fasteners including bolts, screws and other threaded shaft members.
It is an object of the invention to provide novel anti-cross threading fasteners that overcome problems in the prior art, and that are economical to manufacture.
It is another object of the invention to provide novel anti-cross threading fasteners that are easy to assemble, and that are relatively consistently and properly installable, and that are installable under angular and axial misalignment conditions for which prior art anti-cross threading fasteners do not compensate.
It is a further object of the invention to provide novel anti-cross threading fasteners useable in applications susceptible to cross-threading including assembly by unskilled laborers and especially automated fastener assembly operations.
It is a more particular object of the invention to provide novel anti-cross threading fasteners having a threaded shaft portion with a major diameter and a minor diameter, and a leading end shaft portion devoid of screw threads and having a diameter less than the major diameter of the threaded shaft portion. The leading end shaft portion including a tip portion having an at least partially substantially curved surface, and a groove disposed about the shaft between the tip portion and the threaded shaft portion.
It is a related object of the invention to provide novel anti-cross threading fasteners of the type discussed more particularly above having additionally a cylindrical shaft portion between the tip portion and the groove thereof.
It is another more particular object of the invention to provide novel anti-cross threading fasteners having a threaded shaft portion and a portion thereof tapered narrowingly toward a tip portion of the shaft. The screw threads of the tapered threaded shaft portion having a flank angle greater than a flank angle of the screw threads of a nontapered, or remaining, threaded shaft portion.
It is yet another more particular object of the invention to provide novel anti-cross threading fasteners having a threaded shaft portion, and a portion thereof tapering narrowingly toward a tip portion of the shaft. At least some of the screw threads on the tapered threaded shaft portion formed of spaced apart lobes.
It is still another object of the invention to provide novel anti-cross threading fasteners having various combinations of the configurations discussed above.
These and other objects, aspects, features and advantages of the present invention will become more fully apparent upon careful consideration of the following Detailed Description of the Invention and the accompanying Drawings, which may be disproportionate for ease of understanding, wherein like structure and steps are referenced generally by corresponding numerals and indicators.